What Is the Significance of Quark Spin in Quantum Physics?

[cam875]

ive been reading a bit about this and its blowing my mind a bit lol. To think that the spin of a quark has something to do with whether or not something will hapen and the opposite reaction will co-exist in another universe sounds crazy. When it says spin does it mean rotational spin sort of like our planet? I am wondering what real physicists have to say about this topic seeing as I am just a high school student interested I am not really justified in my thought here.

 

[WarPhalange]

"Spin" doesn't really mean something is spinning. Electrons as far as we can tell are point-particles, so it doesn't make sense to say they are spinning.

But particles do have some intrinsic angular momentum associated with them, and we refer to that as spin. It's just there. You can't stop it like you could stop a ball from spinning.

Electrons do "move" around atoms and gain extra angular momentum (like Earth orbiting the Sun), but in that case it depends on which electron shell the atom is in and in what position. And if you take the electron away from the atom, the angular momentum is gone. You can't do that with Spin.

Moreover, all particles have spin. Quarks, Electrons, Protons, and Neutrons have Spin 1/2. Photons and Gluons have Spin 1. There are some neat rules regarding Spin. If two particles have Spin 1/2, they can't be in the same state (i.e. energy level and position). That's why you can only have 2 atoms in the first electron shell of an atom. One electron is Spin +1/2, the other Spin -1/2. When you move up in electron shells, they start going to different places. This is just a flavor, though, and I'm really simplifying it.

But particles do interact with each other based on what their Spin is, because that's where magnetism comes from. So it makes sense that a single particle could determine something, because whether its Spin is +1/2 or -1/2 means it would affect surrounding particles differently.

Of course, it's still just one tiny particle...

 

[muppet]

The point that's more specific to quantum suicide is that the idea of other universes in which events unfold in a different way isn't what could be classed as mainstream science. Rather, it's one of several interpretations of quantum mechanics (which is very, very much a part of mainstream science).
When a physicist looks at the formula for Newton's 2nd law, he can picture in his head how it relates to the world around us. The harder you push something, the faster it ends up moving; the heavier it is, the harder you have to push. When he looks at the eqauations of quantum mechanics, he doesn't know what to think. To take the example of spin, the mathematical description of a single particle might have its spin both +1/2 and -1/2at the same time until you measure to see which it is. It's not just a question of the fact that we don't know which it is, because in many experiments you can see the results of different states of the same particle interacting with each other. There's nothing like it in classical mechanics, and the pictures people come up with to try and explain such strange results are invariably strange themselves as a consequence.

 

[cam875]

wow this is way over my head lol. I am just learning classical physics and stuff that can be observed in real life. Its strange to think that observations made at our level of interaction can be so different than those at the atomic and subatomic world.

 

[DeShark]

Its strange to think that observations made at our level of interaction can be so different than those at the atomic and subatomic world.

This isn't exactly true. For example using quantum mechanics and statistical physics, the correct black body radiation spectrum can be found. The black body spectrum is what we observe in real life and is a quantum mechanical effect. Essentially, all of our observations in real life should be deducable from QM, but in a lot of cases, the computations just involve too many calculations... or at least that's what I'm lead to believe. Some observations can be explained only by quantum mechanics (the photoelectric effect for example) and some can be described by either QM or classical mechanics. However you're right in that the quantum mechanical picture is absurd, but it's important to realize that in most (if not all) cases it's impossible to do experiments with only 5 atoms say. So we use statistics and find out the predicted values in the macroscopic limit. We observe the macroscopic effects and thus show that they agree with the predictions of QM.

 

[Ken G]

However you're right in that the quantum mechanical picture is absurd, but it's important to realize that in most (if not all) cases it's impossible to do experiments with only 5 atoms say.

It would be easy to misinterpret that statement, depending on what definition of the word "absurd" one uses. I would prefer "counterintuitive", that is, counter to the way we interpret our macroscopic experience. We can agree that all interpretations of quantum mechanics run quite contrary to our common interpretations of everyday experience, but saying any more than that makes prejudicial assumptions about the status of our own experience relative to all that's going on in this universe.